HDR Imaging

 

So this technique is pretty stellar.  Using a combination of bracketed exposure, a tripod, and Photoshop, you can achieve an image that’s far closer to what our eye sees than what a camera can capture.  Relatively easy, the real work is done in post – where I have very limited experience.

 

Essentially, the human eye is a wonder to behold.  Every second, your eye is making thousands of small changes and alterations to itself to better discern the world around you.  Focus, brightness, movement, it’s all captured and ‘exposed’ perfectly in real time.  Unfortunately a camera can’t do this.  It can’t look at each detail and perfectly expose every section to get an image that directly represents the location you saw.  So you have to get essentially an average – a shot that best represents the scene as a whole.  But when you do that, you lose the details.

 

One way to get around this is to basically take multiple images and merge them in post.  One would be overexposed to capture the detail in the shadows, one would be normal (the ‘base’ image), and one would be underexposed to get more detail in the highlights.  You would combine these images together and tell the computer to take the base image, and average the curves of all 3 so you get a better representation of the scene.  You could go further and take even more images (5, 7, always an odd number to ensure it’s evenly under/over exposed), each a certain level away from the ‘base’ image, and get an even more accurate representation.

 

This technique has a few drawbacks:

 

• It can only be done on a camera with bracketed exposure, that basically leaves ‘prosumer’ SLR’s and up – although I know some of the entry level SLR’s are starting to pick this feature up
• The subject has to be stationary, if it’s moving, the differing images will throw off the final image
• It has to be done with a tripod, the human hand is just not steady enough
• You can’t make adjustments in the field – it’s all brought together in post (unless you’re carting around a laptop)

In certain situations, I really like it.  It has great potential to do some amazing things – just search on flickr for ‘HDRI’.

What I shot above is this great little spot in the Cleveland Metroparks, and unfortunately it doesn’t really do the technique justice.  The saturation is lost in the leaves because they were moving in the slight breeze, and the sky is ‘bleeding through’ when the images were composited together.  The real difference is in the ground, stairs, and the treebark.  You can see in the image on the right, it was shot at an ISO of 250 for half of a second.  During that time, you can see the noise that built up in the darker areas that the sensor was trying to make sense of.

My next step is to try an HDRI image in RAW format and see what happens.  I may have some time later today during my lunch, so I’ll head out to the park or something – something with a good amount of color and detail.

Ideally, the next step forward would be a digital sensor that was capable of multiple exposures for each shot.  Once the camera shutter was opened, you could divide up the sensor in a matrix pattern to grab different exposure levels for each shot.  Since it’s done digitally, you wouldn’t have to worry about the noise that comes from turning up the ‘gain’ on current analog sensors.  This would allow you to take an image of something – anything, and have it be an HDRI image, thus rendering photos we’ve taken now grainy and obsolete.  They would have greater detail and look absolutely fantastic, since they’ll able to more closely recreate what the human eye is capable of.  Then that technology would be transferred to movies, for obvious reasons.